The invention relates to electronically controlled high resolution light sources of the type typically utilized in high performance light-activated printers, photocomposition systems, chart recorders, and other hard copy devices. More particularly, the invention provides a solid state light source for use in the above noted as well as other similar applications.
It is now the practice that light-activated printers which are capable of 1000 to 2000 point horizontal resolution, frequently use lasers or fiber-optic faceplate cathode ray tubes. Such printers are more versatile than impact printers and can, for instance, print different type styles and sizes at any time, under electronic control.
It is also known to utilize electroluminescent devices in various flat panel display devices. An example of this type of application is disclosed in U.S. Pat. No. 4,110,664 to Asars et al which is assigned to the assignee of the present invention and which is incorporated herein by reference. The flat panel display device of the above-identified patent is an electroluminescent bargraph display system which includes, on a unitary substrate, a plurality of discrete individually controllable adjacent electroluminescent display elements interconnected to a thin film transistor dynamic shift register. Individual stages of the shift register are connected to individual display elements. The electroluminescent display element utilized in such a system is of the type in which one of the electrodes for use with the electroluminescent phosphor is a common light transmissive member. This common electrode is contiguous with the device face and the emissions must pass through this electrode. The structure of such a display panel may also be seen in U.S. Pat. No. 4,006,383 to Luo et al. which is assigned to the assignee of the present invention and which is incorporated herein by reference. The Luo et al. patent teaches an electroluminescent display panel structure in which individual electroluminescent electrodes cover a large area of the panel in order to increase the active display area. Here again, the face of the electroluminescent element is the display surface electrode.
It is an object of this invention to provide an AC excited, thin film electroluminescent line array consisting of individually addressable pixels emitting light from the edge of the line array.
It is a further object of this invention to provide a thin film electroluminescent line array structure having a capacitor for each pixel as an integral component of the structure wherein the phosphor-insulator composite layer serves both as the light-emitting layer for the edge-emitting element and as the capacitor dielectric.
It is another object of this invention to provide a thin film electroluminescent line array which provides adequate light emission and speed of response for the exposure of a photosensitive medium. The line array of this invention in combination with a light-activated printer or similar apparatus renders a device having superiority in resolution, speed, reliability, small size and cost.